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Full text of "Handbook Of Chemical Engineering - I"

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THE TRANSPORTATION OF LIQUIDS
125
The rod stuffing boxes, water pistons, inside packed plungers, and center-or end-packed plungers are generally packed with flexible packing. >istons for oil and for many other substances are fitted with metallic ;   rings.   Metallic  packing is rarely L the pump rods or plungers on ac-of   the   impossibility of   lubricating
The plungers in this case should be
iron to withstand the effect of the 5 packing and the water should be id free from grit.
difficult to pack a pump piston so as ight without causing undue friction. xen the tightness will rapidly wear away e leakage or slip will increase unless t attention is paid to it.
*p Valves.— Small disc valves, made :>er, brass or leather-faced material, ensively used, Figs. 19, 20 and 21. :j"£ in. in diameter are believed to be st suitable, considering quiet working tial cost. The valve seat is screwed .e valve deck, and the stem into the a fine taper. The rubber composition ted so as to be most suitable for the For wet vacuum pumps soft rubber , for low service (75 lb.) medium soft, eral service (150 lb.) medium hard, for sure of 300 lb. hard rubber, but for •es over 125 lb. metal valve discs are
ble to rubber. Hot water demands a special composition. Thickness ber valve disc t = 0.05sVp I where s = span, inches, p = water pres-»ounds per square inch.
I
FIG. 19.—Rubber disc valve.
"Fio.  20.—Brass disc valve.
FIG. 21.—Valves faced with leather.
5 valve area is the free area through the valve seat, and equals the area of the i rcle, Fig. 19, minus the area of the ribs and hub. The water velocity through [ ve area should not be over 222 ft. per minute, which requires a valve area of 45 t of the plunger area at 100 ft. piston speed. Frequently 50 and 60 per cent cified, corresponding to velocities of 200 and 167 ft. per minute, respepervely